1. Field of the Invention
This invention generally relates to data storage facilities for data processing systems and more particularly to a data storage facility that enables the manipulation of common data by first and second data processes.
2. Description of Related Art
The above-cited reference discloses a concept whereby a first physical disk drive, as a first or, standard, mirror stores data and a second physical disk drive, as a BCV mirror in one of two operating modes, stores a mirror copy of the data. That mirror, called a BCV volume in the above-identified reference, can then be split and attached to another application or process that operates on the data independently of operations by another data process on the data in the standard mirror. A controller associated with the data storage facility maintains a list of all changes to the standard mirror in response to a first process and to the second, or BCV, mirror volume while it is attached to the second data process. When it is desired to reestablish synchronization between the mirrors, all data that needs to be altered in the BCV mirror is identified to enable resynchronization.
In such a data storage facility, a write request from the first data process during the first operating, or mirroring mode, transfers to a cache slot in a cache or buffer memory common to the standard BCV mirrors. An acknowledgement is returned to the requesting data process when the write transfer request is stored in the buffer. Thereafter, and in response to an asynchronous process, the write request in the buffer is destaged whereby the associated data transfers from the cache slot to each mirror in separate destaging operations. During the interval between the receipt of a write request in the cache slot and the destaging operation, write requests located in the buffer memory are pending write operations and are designated as xe2x80x9cwrite pendingsxe2x80x9d. At any particular time the buffer may contain up to hundreds or even thousands of write pendings.
As described in the above-identified reference, upon receipt of a split command the BCV mirror stops acting as a mirror for the standard mirror and attaches to the second data process that may be operating in the same host or another host device. However, all devices with which the BCV mirror operates are locked during this shift or transition. While the mirrors are locked, the status of all write pendings and previous write requests are managed as described in the above reference. No further write requests from either data process will be accepted while the lock is in place.
Specifically, after the lock is achieved, a program module performs a number of functions on a track-by-track basis. If a write pending is associated with a track, the module immediately performs the necessary steps for processing that write pending operation. If a previous write operation has occurred and been destaged, the module also performs any updates to track invalid bits. The lock is not released until this process has been completed for all tracks in the logical volume. Consequently, this process can be very time consuming, particularly if there are a large number of write pendings at the time the split occurs. In fact it is possible that the lock may be in place for seconds or even minutes. Such delays are not acceptable in many applications. What is needed is a system that can provide a basic BCV-type function and allow a transfer of a BCV mirror from operation with a first data process to independent operation with a second data process without introducing any significant time delays into the operation of the data process.
Therefore it is an object of this invention to provide a method and apparatus characterized by allowing a storage device to switch between operating modes with minimal interruption to operating data processes.
Another object of this invention is to provide a data storage facility that in a first operating mode provides redundant data storage and in a second operating mode enables one copy of a data set to be accessed by another data process wherein the switch between the first and second operating modes occurs with minimal interruption of either the first or second data processes.
In accordance with one aspect of this invention, a data storage facility enables the manipulation of common data by first and second data processes. The data storage facility includes first and second data stores and a buffer whereby a write request is processed by transferring the write request to the buffer and thereafter transferring data to a data store. A control for the data storage facility includes first and second control modules. The first control module transfers the operation of the storage facility from a first operating mode to a second operating mode. During the first operating mode, the second data store acts as mirror for data in the first data store and is available to the first data process. During the second operating mode the second data store becomes available to the second data process. The second control module responds to the transfer effected by the first control module by thereafter performing any processing required by write requests processed during the first operating mode including write requests in the buffer at the time of the shift to the second operating mode. This processing occurs in parallel with and transparently to any interaction with the first and second data stores and the first and second data processes, respectively.
In accordance with another aspect of this invention, data transfers in a data processing system can occur between first and second data processes and a data storage facility with first and second data stores and a buffer. The data storage facility responds to a predetermined transfer request by transferring data to a write pending location in the buffer and thereafter transferring the corresponding data to the data stores. During a first operating mode the first and second data stores act as mirror memories, and the system maintains an identification of all write operations that occur including write pending operations. When a predetermined command is received, the system connects the second data store for operation with the second data process in parallel with continued operations between the first data store and the first data process. Data transfer requests for data in a write pending data location in the list in either of the first and second data stores effects a transfer of the data to the second data store.